Field of the Invention
The present invention relates to an intermediate phase continuous variable valve timing (hereafter, referred to as “CVVT”) with an advance timing compensating system and a stopper and, more particularly, to an intermediate phase adjustment apparatus of an CVVT that always achieves self-lock regardless of the RPM of an engine and hydraulic conditions by balancing hydraulic pressure of an advancing chamber and a retarding chamber.
Description of the Related Art
In general, an CVVT is applied to a vehicle to reduce exhaust gas and improve fuel efficiency and output. Recently, intermediate phase CVVT systems for removing limits in response and operation area of the existing CVVT systems are increasingly being used. Intermediate phase CVVTs control the position of a cam not at the most advanced (intake) position and the most retarded (exhaust) position, but at an intermediate position, so response is quick and the use area of a cam can be increased, and accordingly, fuel efficiency is improved and exhaust gas is reduced.
In an intermediate phase CVVT, a lock pin on the rotor is locked into a lock pin hole between the advancing chamber and the retarding chamber while the RPM of an engine is reduced, thereby preparing for later engine start. The action that the lock pin is automatically locked into the lock pin hole while the RPM of an engine is reduced is called ‘self-lock’. The self-lock is a function that allows an CVVT to mechanically return to an accurate position without specific adjustment so that operational stability of an engine can be maintained in periods where the CVVT system is not used, that is, when the engine is idling or is started.
In order to compensate for a difference in cam torque between advancing and retarding in self-lock, as shown in FIG. 1, a spring 50 is provided and a stopper 70 for controlling rotational amount of the spring 50 is additionally provided.
However, when the spring 50 and the stopper 70 are used, a difference Θ depending on the mounting position of the stopper 70 is generated maximally by 0.8 degrees, so a hydraulic pressure difference is generated between the advancing chamber 11 and the retarding chamber 13 due to a difference of an engine, a load difference of an advancing timing compensating system, and a mounting position difference of the stopper. Further, when the hydraulic pressure difference is too large, ensuring an intermediate position of a lock pin 80 for self-lock may be difficult.
Therefore, when control fails due to malfunction of a control unit, there is a need for an intermediate phase adjustment apparatus of an CVVT for balancing hydraulic pressure between an advancing chamber and a retarding chamber for self-lock of an CVVT.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.